For production of semifinished products and finished products from polyvinyl chloride, plasticizers are used on a large scale, these typically being combined with the polymer pellets during a mixing and heating operation according to the prior art, such that the polymer pellets either dissolve in the plasticizer or the plasticizer is absorbed by the polymer pellets. The polymer plasticized in this way is then processed further by extrusion or other forming techniques to give semifinished products or finished products. A comprehensive description of the prior art can be found, for example, in C. E. Wilkes, J. W. Summers, C. A. Daniels; “PVC Handbook”, Hanser-Verlag 2005. The efficiency of the plasticizers is typically measured by the processing properties that they permit during compounding and by the physicochemical properties of the material after processing. Important properties are, for example, low volatility during processing to give the compound, rapid diffusion capacity into the polymer matrix, good thermal stability with a view to resistance to decomposition or discoloration, and a good profile of mechanical properties, in which a favourable combination of breaking strength, hardness and bending strength is typically required. In addition, favourable low-temperature properties may be called for if the material is used to produce, for example, mouldings which are used in cryotechnology, for example. Further demands with regard to the toxicological properties of the processing aids used may also be made on materials which are used in contact with food and drink, in medical technology, or else for production of children's toys.
Phthalic esters which have been used for some time as plasticizers impart a favourable performance profile to the PVC materials with low production costs, and these are therefore counted among the universal plasticizers. These include, for example, dioctyl phthalate (DOP), diisononyl phthalate (DINP) or else diisodecyl phthalate (DIDP). With specific plasticizers, however, it is possible to influence certain desirable properties, for example low-temperature bending resistance or impact resistance, thermal stability, fire resistance or migration resistance. These specialty plasticizers include, for example, the esters of mono- or tribasic aromatic carboxylic acids or di- or polybasic aliphatic carboxylic acids.
It is additionally known that universal plasticizers can be processed in combination with what are called extenders in order to reduce the manufacturing costs of PVC component production. The extenders used are, for example, naphtha-based hydrocarbons, aliphatic hydrocarbons or else chlorinated hydrocarbons, the latter additionally exerting a flame-retarding effect. Such extenders generally have only limited compatibility with the PVC polymer matrix and have a tendency to migrate out of the moulding in the course of ageing processes or to separate from the polymer matrix in the moulding. The result is generally unwanted release to the environment, and also an unwanted reduction in the mechanical properties of the moulding, which is generally manifested in the form of embrittlement.
However, not only the extenders result in unwanted separation and migration out of the PVC component; the primary plasticizers also exhibit a more or less marked migration tendency which can lead to unwanted degradation of the material properties in the course of component ageing.
The group of the phthalic esters which have been used over a long period as plasticizers in the PVC-processing industry, the protagonist of which can be regarded as dioctyl phthalate, has additionally long been the subject of intensive toxicological studies, since it is suspected that they can adversely affect the human hormone system as what are called endocrine disruptors. The possible influence thereof on human health has led to intensive, controversial discussions which ended, for example, in bans from regulators on the use of dioctyl phthalate in soft toys for infants. Various phthalates have likewise been removed from formulations for cosmetic applications (cf., for example: M. Ittershagen, “Phthalates—Useful Plasticizers with undesired Properties”, 2007 status report of the Federal Environment Agency of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety of the Federal Republic of Germany). The discussion about the influence of migrating plasticizers on the environment and on human health, but also the long-term fitness for use of PVC articles, has led to a broad interest in migration-resistant, phthalate-free plasticizers.
There has therefore been a constant major interest in industry in plasticizers having a favourable combination of processing properties during compounding and moulding production, such as good heat, migration and elution resistance, which allow development of specific product properties such as favourable low-temperature properties and additionally have a favourable toxicological profile.
In order to achieve a balanced profile of properties for the plasticizer used, mixtures of various primary plasticizers are also used. WO 2007/144831 A2 discloses flexible hoses for the transport of liquid food and drink. In order to ensure sufficient flexibility of the hose on the one hand but to minimize the migration of the auxiliaries into the food and drink on the other hand, mixtures of trimellitates and adipates or mixtures of monomeric and polymeric adipates, for example, are used as plasticizers. According to WO 2012/075164 A2, PVC plastisol is processed by the spraying technique to give soft PVC articles, the plasticizer used being a mixture of trimellitates and a second plasticizer such as adipates or sebacates.
EP 1 672 013 A1 discloses ester mixtures comprising a mixture of esterification products of polyether polyols and aromatic monocarboxylic acids and aliphatic monocarboxylic acids. In addition, tri(2-ethylhexyl)trimellitate may also be present as a further plasticizer.
EP 1 983 024 A1 discloses ester mixtures comprising alkylbenzyl esters of aromatic tri- and tetracarboxylic acids and polybenzyl esters of aromatic tri- and tetracarboxylic acids. Trioctyl trimellitate may also be present as a further plasticizer. WO 2007/101968 A2 relates to PVC compositions plasticized with trioctyl trimellitate.
The known trimellitic ester-containing plasticizer mixtures are not necessarily the optimal solution in each case for the required field of use of the plastic article, and so there is a constant demand for improved plasticizer mixtures.
It has been found that, surprisingly, such a profile of demands can be fulfilled by mixtures of trimellitic esters and polyether polyol esters.